The lymphatics represent the third circulation in the body and are an important route of spread for tumors. Lymphangiogenesis is a property of some tumors that allows them to propagate via the lymphatics. This process has been difficult to study because the lymphatics are small and inaccessible. However, by injecting various kinds of macromolecular contrast agents, including radiolabeled, optically labeled and magnetically labeled it is possible to identify the lymphatics and their drainage patterns. Moreover, the knowledge gained in this process has implications for the diagnosis and management of primary and secondary lymphedema, which can be a serious complication of cancer therapy. Finally, the development of macromolecular contrast agents has implications for other diseases. The MIP is investigating the role of the lymphatics in cancer using imaging methods. We have found that macromolecular agents of between 5-10nm in diameter are ideal for studying the lymphatics based on their rapid uptake and transit to the sentinel nodes. Sentinel node imaging is of importance because current methods rely on cumbersome blue dyes and radioactive sulfur colloid. We have developed a dendrimer that is dual labeled for MRI imaging and optical imaging that would allow the identification of the sentinel node without ionizing radiation using MRI and optical imaging. By comparing different sized dendrimers optimization of the lymphatic agent was achieved. We found that very small agents leaked from the lymphatics and were unsatisfactory whereas large agents were too slow. Therefore, the Generation 6 dendrimer loaded with Gadolinium and an optical fluorophore appears ideal. Working others, we have developed and tested dendrimers with new syntheses that should simplify the chemistry for possible clinical translation. We have also used IgG as a carrier molecule for lymphatic imaging and shown it to be a biocompatible and suitably sized for lymphatic imaging. Furthermore, we are investigating the FDA-approved drug Ablavar for lymphatic imaging as this gadolinium chelate binds albumin and effectively becomes macromolecular. We are currently working on a dendrimer loaded with Gadolinium for potential human use. This agent uses medical grade dendrimers with a high affinity chelate, DOTA. This could be useful in the preoperative mapping of lymphatic obstruction and malformations. We have found that a commercially available, FDA approved Gadolinium based agent, gadofosveset (Ablavar) may be sufficient to identify the lymphatic channels because it binds to albumin creating a virtual macromolecule. We have employed two color QDs to investigate the drainage of the breast and arm to the axillary lymph nodes and found that some mice had independent drainage systems whereas other mice demonstrated dual draining nodes , i.e. nodes that partly drained the breast and partly drained the limb. Additionally we have explored the use of up to 5 QDs of differing wavelength simultaneously in order to establish the complex lymphatic drainage patterns in the head and neck. We have been collaborating with Boston Childrens Hospital to develop a MR contrast agent for use in human children with primary lymphedema. Ferumoxytol is an iron containing oxide that accumulates in normal nodes. We are testing this agent in patients with GU malignancies to see if it is suitable for detecting lymph node metastases. A preliminary study of 20 patients with prostate cancer has concluded and a new study will be underway. We are collaborating with the HIV/AIDS group to understand the lymphatic drainage of the colon. We are developing a method of identifying the relevant lymph nodes by identifying the sentinel nodes related to areas of inflammation. In understanding the drainage patterns on imaging it may be possible to better understand the mechanisms of HIV induced colitis. Additionally we are studying structural imaging changes in chronically infected animals with SIV demonstrating fibrosis.